1. Field of the Invention
The present invention relates generally to a key structure, a key input device, and a character input method in an apparatus for inputting digits and characters using a keypad, and in particular, to a method for representing all characters available in a known 3×4 key input scheme by use of a small number of keys.
2. Description of the Related Art
Many key input devices and character input methods have been developed in the field of mobile radio terminals in order to easily represent intended characters, while minimizing the area of the key input devices along with the trend of reducing the size of the terminal. They include the known 3×4 key input scheme, a 2-way slide key input scheme, and a 4-way key input scheme. The latter two schemes were suggested as alternatives for the 3×4 key input scheme.
Due to the minimum space requirement of a keypad, the 3×4 key input scheme was an obstacle to miniaturization of mobile radio terminals. “Minimum space requirement” refers to a minimum space required for precise selection of an intended key and isolation of the key from its adjacent keys on a keypad when a user manipulates the keypad. That is, for a terminal to recognize a key pressed by the user, the key should be spaced from its adjacent keys by a distance enough to prevent the key pressing from influencing the adjacent keys. The 2-way slide key input scheme and the 4-way key input scheme appear to be favorable candidates for the replacement of the 3×4 key input scheme in that they contribute to the reduction of the minimum space requirement of the keypad. Despite this advantage, their key input mechanisms cause a user inconvenience and time delay in key input. Particularly, a longer time is required to enter Korean alphabet characters (Hangul).